A radioimmunoassay for urinary kinins was developed and applied to the assay of kinins in human urine. Prekallikrein and urokininogen were discovered in human urine. Prekallikrein probably arises from the distal tubule. The half-life of kinins in urine is 2-4 hours. BIBLIOGRAPHIC REFERENCES: Geller, R.G., Yoshida, H., Beaven, M.A., Horakova, Z., Atkins, F.L., Yamabe, H., and Pisano, J.J.: Pharmacologically Active Substances in Venoms of the Bald-Faced Horner, Vespula (Dolichovespula) Maculata, and the Yellow Jacket, Vespula (Vespula) Maculifrons. Toxicon 14: 27-33, 1976. Hial, V., Keiser, H.R., and Pisano, J.J.: Origin and Content of Methionyl-Lysyl-Bradykinin, Lysyl-Bradykinin and Bradykinin in Human Urine. Biochem. Pharmacol: 25: 2499-2503, 1976.